1. Field of the Invention
The present invention relates to a liquid jetting apparatus such as an ink-jet recording apparatus which records an image on a recording medium by jetting an ink from a jetting head.
2. Description of the Related Art
For example, in an ink-jet recording apparatuses described in Japanese Patent Application Laid-open No. H5-92578, when a viscosity of an ink in a nozzle hole of a jetting head is increased due to not using the apparatus for a long time, or when there is a blocking of the nozzle hole due to mixing of an impurity etc., a positive-pressure purge operation is carried out. In the positive-pressure purge operation, an inside of an ink tank which communicates with the jetting head is pressurized, and the ink is jetted forcibly from the nozzle holes, and a function of the jetting head is recovered by the positive-pressure purge operation.
Incidentally, when a temperature change is occurred in the apparatus, an excessive positive pressure might be generated inside the ink tank of a fixed volume. When the excessive positive pressure is generated, the positive pressure is propagated from the ink tank to the nozzle hole of the jetting head, and a favorable meniscus in the nozzle hole might be destroyed. In an ink-jet recording apparatus described in Japanese Patent Application Laid-open No. 2005-169892, an atmosphere opening hole (an air vent hole) is formed in the ink tank, and this atmosphere opening hole is covered by a positive-pressure control valve on which a bias is applied by a spring, in a direction of closing. According to such structure, only when the excessive positive pressure is generated inside the ink tank, the positive-pressure control valve moves against the bias of the spring. Accordingly, the atmosphere opening hole is opened, and a pressure fluctuation (pressure change) in the ink tank is suppressed.